head_style.rb in bootstrap-email-1.4.0

- old
+ new

@@ -18,9 +18,10 @@
         HTML
       end
 
       def purged_css_from_head
         default, custom = BootstrapEmail::SassCache.compile('bootstrap-head', @config).split('/*! allow_purge_after */')
+        custom ||= ''
         # get each CSS declaration
         custom.scan(/\w*\.[\w\-]*[\s\S\n]+?(?=})}{1}/).each do |group|
           # get the first class for each comma separated CSS declaration
           exist = group.scan(/(\.[\w\-]*).*?((,+?)|{+?)/).map(&:first).uniq.any? do |selector|
             !doc.at_css(selector).nil?